The invention relates to an ultrasonic probe, more specifically for manual inspection. It has a housing which accommodates an ultrasonic crystal and has a contact surface for contact with the surface of a body to be inspected.
Extensive prior art exists with respect to such type ultrasonic probes. In ultrasonic inspection one would like to know with the greatest possible accuracy the location on the body to be inspected that corresponds to the ultrasonic test results. Meaning, one would like to associate an ultrasonic test result with a corresponding location. As a result, one aims at being capable of accurately localizing a detected flaw during weld testing. In the same way, it is also desirable to exactly know the location on the container or pipe at which a predetermined ultrasonic test result was determined during determination of remaining wall thickness of a tube or a container. This means that not only the ultrasonic signal is to be known, but the respective position of the ultrasonic probe on the surface of the body to be inspected as well.
According to prior art, systems exist that determine the position of the ultrasonic probe, e.g., as a position of the probe in two or three axes relative to a location, as the measurement is being started. For the time being, a resolution of 0.1 mm is achieved for longitudinal movements and 0.1xc2x0 for rotational movements. Together with the relative position data and the respective ultrasonic test result the absolute position of a flaw may be determined with accuracy. As a result, repair work or systematic monitoring of defective sites may be performed profitably and selectively.
The currently used methods of determining the position data in manual ultrasonic inspection have some major disadvantages. For detecting the position, additional electronic component parts such as e.g., airborne sound sensors and/or mechanical guides are needed, which have ergonomic drawbacks. The mechanical parts may wear, the airborne sound sensors are relative large in size, more specifically to install and to adjust. The cost of the known methods and of the devices used for this purpose is high.
In view thereof it is an object of the present invention to produce an ultrasonic probe that ascertains and outputs position coordinates on the body to be inspected as a function of a location known as measurement starts. The disadvantages of the hereto before known systems are to be avoided.
The solution to this object is an ultrasonic probe, more specifically for manual inspection
with a housing that accommodates an ultrasonic crystal and has a contact surface for contact with the surface of a body to be inspected,
with at least one digital camera that is assigned to the housing, is oriented in such a manner that it acquires the surface of the body and periodically delivers an electronic image of respective portions of the body""s surface,
with a circuit for image processing that is comprised of an image memory for at least one electronic image acquired by the digital camera, that has a comparator which compares two electronic images, acquired at different times by the digital camera, of overlapping portions of the body""s surface and determines therefrom the displacement of the housing relative to the surface, which is then output, and
with a motion memory that stores the displacement of the housing starting from a location at the beginning of the measurement and contains the actual position of the housing with respect to said location.
To begin with, this ultrasonic probe is a classical ultrasonic probe having the usual features of a such type probe. By way of example the reader is referred to the DE-book J. Krautkrxc3xa4mer and K. Krautkrxc3xa4mer xe2x80x9cWerkstoffprxc3xcfung mit Ultraschallxe2x80x9d (xe2x80x9cMaterial Inspection with Ultrasoundsxe2x80x9d), 6th edition, Springer-Verlag. Accordingly, the ultrasonic probe may be utilized like a conventional ultrasonic probe. It is for example configured as a double transducer probe.
In addition, the ultrasonic probe in accordance with the invention has means serving to indicate the respective position on the surface of the body to be inspected with regard to a location that was known at the beginning of the measurement.
For this purpose, at least one digital camera is firmly connected to the housing. The digital camera is preferably disposed in the housing. It is oriented so as to acquire the surface of the body to be inspected. It is thereby to deliver an image of this surface in the nearest possible proximity to the site at which a central beam of the active sound element traverses the surface.
By means of this digital camera, an electronic image (frame) is periodically acquired of that surface portion that is just located beneath the lens of the digital camera, meaning that lies in the plane of the object. This portion is a relatively small portion of the overall surface of the body to be inspected. The portion may have dimensions of a few mm, e.g., 2xc3x972 to 4xc3x974 mm. At predetermined fixed time intervals, the digital camera preferably takes an image of the respective one of the surface portions.
In the circuit for image processing connected downstream the digital camera, at least one image taken with the digital camera is stored in an image memory. In the comparator this image is compared with an image the digital camera acquired later. The comparator displaces the two electronic images to find a match with each other, meaning until corresponding image zones are coinciding. This means that the interval of time between two electronic images to be compared being taken is not allowed to be greater than the time during which the housing is displaced by a distance that is greater than the diagonal of the acquired electronic image. In this case the electronic images to be compared do not contain any matching portions any longer so that comparison is not possible.
The actual displacement on the surface of the body to be inspected may be computed from the necessary relative displacement of the two individual images compared in the comparator to find a match with each other. The image scale of the optics is substantially taken into consideration in this computation. Accordingly, a position signal may be delivered that is indicative of the displacement of the probe between the time at which the first electronic image was taken and the time at which the second electronic image was taken. The respective actual position of the probe on the surface of the body to be inspected is obtained from the sum of the individual displacement information data starting from the location at the beginning of the measurement.
Accordingly, an optical system forms the basis for position detection. The digital cameras are preferably equipped with CCD sensors. The object field of the digital camera is preferably assigned a lighting element for illuminating the surface portion to be acquired. Upon motion of the probe, the actual position is determined from the position information data contained in the motion memory.
Nowadays, the electronic and optical means utilized for determining the position are available in very small sizes and at low cost as well. As a result, the complete image evaluation unit may be accommodated within a housing of a conventional ultrasonic probe. More specifically, with the ultrasonic probe of the invention, the evaluation of spatially small flaws may be carried out parallel to the surface of the body to be inspected. In testing welds such as in tubes, pipelines or in the construction of containers and boilers, the locations of the respective sites may be indicated in a test result.
The use of double transducer probes allows for simplified application in determining location coordinates. The transmit/receive crystal of the ultrasonic probe is separately accommodated within a housing, the separation being provided by an attenuation web. At least one digital camera permits to determine in the simplest manner the position of two axes specifically for these probes. The remaining wall thickness of curved tubes may thus be determined advantageously.
The distance travelled is summed in the motion memory. Inspections may thus be performed profitably, with enhanced ergonomics. An inspector guiding the probe may perform the test at optimum conditions. No parts are subject to wear and inspection safety is considerably increased as compared to inspection without additional information concerning the location coordinates. As compared to mechanical systems for position acquisition, costs are saved up to 60%. Exhaustive documentation of the inspection is possible.
In a particularly preferred development, two digital cameras are provided, said cameras being spaced apart on the housing, each of them having a circuit for image processing of its own connected downstream thereof, and being provided with an evaluation step for rotations at which the outputs of the two circuits for image processing are applied. A rotation of the housing relative to a previous rotational condition is determined from the various information about the position of the housing obtained from said two circuits for image processing and is output. A rotation memory contains the rotation information starting from a rotational condition at the beginning of the measurement.
When two digital cameras are being used, the position of the angle of rotation of the probe about its own axis may be very easily determined by way of transformation functions. Although it would be possible in principle to acquire this position with only one camera as well, this would require the image comparison within the comparator to be performed in such a manner that the electronic images are not only displaced in pixel bounds relative to one another in but two directions until a match is achieved for a partial region thereof, but that the two compared electronic images are also rotated relative to each other. This considerably increases the expense and time needed for the electronic evaluation in the comparator. Inasmuch, to install a second digital camera is a simple and advantageous solution.
In the embodiment with two digital cameras, there is provided a rotation memory that stores the determined rotation information starting from the condition at the beginning of the measurement. In this way, the respective overall rotation as compared to the condition at the beginning of the measurement is known.
In a preferred development there is provided a signal memory which is permanently assigned to the motion memory and which stores the ultrasonic information available at a respective position together with the position information. The result of the ultrasonic inspection may thus be readily accessed. An evaluation may be performed in different ways. It is thereby particularly preferred if, whenever a critical ultrasonic inspection test result is obtained, e.g., whenever a preset threshold is exceeded in the signal, this condition is shown on a display. Defective sites and other imperfections in the body to be inspected are thus displayed on a monitor for example. The information obtained may thus be readily processed further.
A start switch proved very advantageous. It is preferably disposed on the housing of the ultrasonic probe. It may concurrently be assigned various functions that are independent of each other. Upon actuation of the start switch, the motion memory is reset and restarts summing up the subsequently delivered motion information. The start switch may also serve to start the optical and electronic unit for position acquisition. As a result thereof, said unit may be in a low-current off function before that. Also, the lighting means may be switched off.
It is possible but not necessary to provide a coupling means, water for example, between the ultrasonic probe and the surface of the body to be inspected. The function of optical position detection proved not to be affected thereby.